I too wish Alfred Workflows had a built in auto-updater for workflows
I will point out there is probably a decent reason Alfred doesn't do this though. Workflows are unvetted 3rd party code. It gets sticky if Alfred is facilitating updates and those updates could possibly be malicious. Still, Chrome does this with extensions, and malicious injections while not unheard of are pretty rare.
I feel like Alfred ought to at least provide the update notification hook, and tooling for workflow updates though. Then require users to manually click to update workflows with a disclaimer or something.
The reason is that my workflows are often broken due to being out of date, and that in turn results in a poor perception of Alfred itself.